Interlocked motor system



Marci; 12, 1946.

S. READ, JR

IKTERLOGKED MOTOR SYSTEM Original Fild Sept. 30, 1941 2 Shefcs-Sheet 1 il W 3nnentor Gidfief;{ Read, Jr:

(Ittomeg March 12, 1946. s, A JR I 7 2,396,530

INTERLOCKED MOTOR SYSTEM Original Filed Sept. 30, 1.941 2 Sheets-Sheet 20 U g o 0 Q 3 r R m 3 Q $138950 7110100110311! HTQA/b Zmnentor SidneyHead, Jr.

attorney Patented Mar. 12, 1946 INTE-RLOCKED MQTOR SYSTEM Sidney Read,In, Indianapolis, Incl, assignor to Radio Corporation-of America, a,corporation of Delaware.

Original application September. 30,, 1941, Serial, No. 413,028. Dividedand'this'application May 30; 1942; Serial- No. 445,189

Claims.

This inventionrelates to an interlocked motor system and moreparticularly to an electrical motor system of the multiphase type inwhich the motors may be interlocked at a standstill and brought to anydesired speed while maintaining the interlocked relation between themwith a minimum of oscillation and with no slippage Within the powerlimits of the motors, This application is a division of my applicationSerial No. 413,028, filed September 30, 1941.

Various types of interlocking motors haveheretofore been proposed andthese have been more or less satisfactory for many purposes. Forsomepurposes, however, the prior art motors have not been completelysatisfactory due to the limitations on the degree of interlockingsecured at various operating speeds; For example, in the well knownSelsyn type of' motor system both phase-wound rotors and stators areused. This arrangement gives a very satisfactory interlock at low speedsbut as the speed increases the degree of interlock falls off so that atsynchronous speed there is no interlock between the several motors.

In another system the several synchronous motors are driven fromanalternator, the speed of which can be varied, and this arrangement hasthe opposite. defect in operation. Although the several motors andthealternator operate in synchronism at normal running speeds when thealternator is'first started, there is no voltage and therefore nointerlock at low speeds and the motors may slipseveral poles or evenseveral revolutions before coming into synchronism.

In still a third arrangement, a battery bank may be used and multi-phasecurrent supplied to the motors through an appropriate commutatingdevice. In this arrangement, the same faults arise as in the Selsynarrangement although for a different reason. If the motors, voltages andcircuit resistances are so arranged that a satisfactory interlock issecured at low speeds, then as the speed increases the motor impedancerises and the degree. of interlock falls off while if the motorimpedances and battery voltages are so arranged. that satisfactoryinterlock is secured at a fairly high running speed, then resistancesmust be inserted in the circuit in starting and there is a tendency forthe motors to slip out of phase when these resistances are switched outof or into the circuit.

In the present arrangement a special type of polyphase distributor isprovided which applies a substantially uniform interlock current to; the

motors at all operating speeds and above a certain point the voltageapplied rises with the frequency' so that the current through the, motorwindings remains substantially constant.

One object of the invention isto provide a synchronous motor system inwhich the motors: are interlocked at standstill and'all running speeds:

Another object of the" invention is'to provide an interlocked motorsystem in which the degree of interlock does not fall off with the motorspeed.

Another object of the invention is to provide an improved polyphase-distributor;

Anotherobject of the invention is to provide a motor system which maybestarted as an interlocked motor system which maybe brought tosynchronous speed interlocked andwhich may thereafter be operated as asynchronous motor system.

Another object of the invention is to provide a motor system usingmotors which may be operated either in an interlock system or which maybe independently operated as synchronous motors directly from the line;

Other and incidental objects of the invention will be" apparent to thoseskilled in the-art from a reading of the following specification and aninspection of the accompanying drawings, in which- Figure l is aschematic diagram of my improved motor system including the improvedpolyphase distributor,

Figure 2 is a curve showing the voltage versus frequency characteristicsof the improved distributor;

Figure 3 is a curve showing the restoration of the type of motor used inmy improved system to original angular position after being deflected apredetermined amount,

Figure 4 is a curve corresponding to Figure 3 but for a motor of theprior art, and

Figure 5 is a series of curves of angular displacement plotted againsttorque for different types of synchronous motors;

Referring to Fig. 1, power from a polyphase source which might, by wayof example, be 220 volts, three-phase, -cycle A.-C., is supplied throughthe leads Ill, 1! and 2. The reason for reference to this particularfrequency and voltage is that it is now the type most generally used forthe synchronous operation of sound picture apparatus and thereforeillustrates a typical commercially available power supply. It will beunderstood, however, that the invention is not limited as tothe numberof phases, voltageor frequency; This current-is supplied through theswitches l3 and M and their connecting means to the delta connectedstator windings I5 of the synchronous motor schematically indicated atl5, l5 which serves to drive the polyphase distributor generallyindicated at 5B. A suitable D.-C. voltage is applied in a conventionalmanner to the rotating field winding l6. Power passing through theswitch it is also supplied through appropriate leads to the collectorrings 2i, 22 and 23 of the polyphase distributor.

The rotor it of the driving motor drives the shaft 20 of the distributorwhich also carries a magnetic brake including the winding i'l, the brakemember it and the brake drum [9. This brake is of the type which remainsapplied so long as there is no current in the winding l1. Current fromthe collector ring is supplied through the Y-connected rotor windings2d, 25, 26 to the closed winding 2i connected to the commutator Currentfrom the commutator 28 is picked up by the brushes 29, Eli and iiispaced 120 apart and fed through stator windings 32, 33 and 3a to themotors to be driven in synchronism through the switch 35.

If the switches I3 and It are closed, the switch 35 being open, thebrake is will be released and the synchronous motor i5, is will bringthe shaft 20 up to synchronous speed. At this speed the windings 2 25,26, 2' are rotating at the same rate as the electrical field and directcurrent will be supplied through the brushes 29, 3%? and 38. In theinstance above given, the windings should be so proportioned that thisdirect current is of the order of 20 to 30 volts for driving typicalvariable reluctance synchronous motors of a size of the order of /6horsepower such as are used in operating sound picture apparatus.

The motors indicated at 36, 31 and 39 in Fig. 1 are of the type having Aconnected wound rotors indicated at ti and t2, D.-C. stators indicatedat 65, l? and i8 and damping windings 43, 44 and 15.

The system is not limited to the use of the particular type of motorsshown, as any of the usual types of polyphase synchronous motors may beused, and it is not even necessary that all the motors of an associatedgroup be of the same type. Whichever type of motors is used, theresistance to reactance ratio of all the motors of the group should beproperly matched to the distributor characteristics.

In the operation of the system the switch 35 is left open until thepolyphase distributor 58 has come up to speed. The switch 35 is thenmoved from the open upper position downwardly to the center or closedportion shown in the drawings. Direct current is thereby supplied to thewindings M, ii and 42 looking these rotors in position. In order tobring the motors up to he desired speed the switch it is opened therebyremoving the driving power from the shaft All and applying the brake it.Under this condition the rotor of the distributor 53 slows down at aspeed determined by its own inertia, the inertia of the driven systemand the effectiveness of the brake l3, and as this rotor slows down thespeed of the rotors 4%, ri and 52 is increased. When the rotor 29 hascome to complete stop, alternating current is supplied through thebrushes 29, 3 and 3! and windings 32, 33 and i i and the motors 36, 3?and 38 operate at synchronous speed, the distributor 5t serving as atransformer of proper ratio, in the present instance 1:1.

If it is desired thereafter to eliminate the distributor 59 from thecircuit, the switch 35 may be moved downward to its third positionthereby connecting the motors 36, er and 38 directly to the power sourceHi, I i and i2 when they operate as synchronous motors directly from thepower line, but still exactly in step.

An appropriate phase inductor or equivalent phasing device may beconnected across the contacts of the switch 35 in order to determine thephase relation between the output of the polyphase distributor and thepower supply line lil-l ll2. The rotor of the polyphase distributor maybe rotated manually or in some equivalent manner to bring its outputinto proper phase relation with the line if it is desired to switchthese motors directly onto the line rather than to let them run off thedistributor.

When it is not material whether the motors remain synchronous instopping or not, the motors may be stopped merely by opening the powerswitch. If, however, it is desired to maintain the motors in theirpredetermined angular relation the reverse steps may be gone through,the motors being operated through the distributor which remains at astandstill and the distributor 50 then being brought to synchronousspeed by closing the switch it when the motors will be brought to astandstill and remain interlocked.

The relative characteristics of this type of motor system are shown inFigures 2 to 5. As shown in Fig. 2 a certain chosen voltage is producedat zero frequency (or D. C.) and this voltage which, as described above,with the type of one-sixth horsepower, 220-vo1t motors, used in soundpicture recording, may be of the order of 20 to 40 volts, provides theinterlock at standstill. As the distributor speed is reduced and themotor speed increases, the voltage increases slightly as rotation beginsand thereafter the voltage is proportional to frequency So that aconstant interlock current is maintained and this is true evenif themotors are operated above synchronous speed. For example, in theoperation shown in Fig. 1 the polyphase distributor may be brought to astandstill when the motors 355, 3'8 and 38 will be operating atsynchronous speed. Any two of the leads [5, i i and i2 may then bereversed by an appropriate switch between the switch it and the motor[5, Iii and the motor i5, iii may then be started in the oppositedirection to its original direction of rotation whereupon the speed ofrotation of the distributor will be added to the speed of rotation ofthe electrical field and if the motor driving the distributor be of thesynchronous type the motors 35, Si and may then be brought up to twicesynchronous speed and over this entire speed range the voltage frequencycharacteristic illustrated in 2 will be followed.

The restoration characteristic of this motor system when deflected isshown in Fig, 3. In this figure the no load position is indicated by thelower line 5! which indicates the slight variations in speed of themotor as recorded by an oscillograph. When the motor is displaced inphase to the line 52 by loading through an angle of a little over fivedegrees it is immediately restored to the no load position with nooscillation whatever when the load is removed. This particular curve wastaken from a standard onesixth horsepower reluctance synchronous motor,operating at 1800 R. P. M., and driven from three-phase current atcycles, this being the most desirable type of motor from the standpointof stability.

The curve in Fig. 4 corresponds to that shown in Fig. 3, but shows thecharacteristics of a onequarter horsepower Selsyn motor, operating at1200 R. P. M. It will be noted that when this motor is deflected fivemechanical degrees and then released, large oscillations about the noload position follow which gradually decrease.

In Fig. the stiffness characteristic of various types of synchronousmotors are shown plotted in terms of angle of mechanical deflectionagainst the torque in ounce inches as applied to the motor shaft. Thecurve marked A is for a one-quarter horsepower 1200 R. P. M. Selsynmotor but with the torque and deflection referred to 1800 R. P. M. Thecurved marked C is for a one-sixth horsepower, 1800 R. P. M. variablereluctance synchronous motor in synchronous operation in accordance withFig. 1.

It will be apparent to those skilled in the art that the usefulness ofmy improved motor system is not limited to the operation of smallmechanical devices in synchronism but that it may also be used in thesame manner as any of the more usual types of telemotor or telemetricdevices. My system has the further advantage over ordinary synchronousmotor arrangements that the driven motors need not be of the same sizeor type so long as their ratio of resistance to inductance is the same.For example, some of the motors may be of very high horsepower, such aswould be used to control the position of a ships rudder, or thedirection of heavy ordnance while other motors actuated from the samedistributor might be relatively small and light and serve to controlposition indicators such as rudder position indicators or gun sights. Inthis arrangement it will be apparent that instead of the indicatingmechanism controlling the full power to be applied to the controlleddevice, the power control would be entirely through the distributor 50While the indicators or signs would be actuated synchronous with thecontrol devices and assume a position corresponding to the position ofthe controlled devices.

I claim as my invention:

1. A polyphase distributor system for controlling the starting of atleast one synchronous motor, said distributor comprising a plurality ofwindings Y-connected to a closed winding, commutator segments connectedto said closed windin said Y-connected windings, said closed winding,and said commutator segments constituting the rotor of said distributor,a plurality of windings equal in number to said first plurality of Y-connected windings, and a plurality of brushes contacting saidcommutator segments, said second mentioned plurality of windingsconstituting the stator of said distributor.

2. A polyphase distributor system for controlling the starting of one ormore synchronous mo tors, said distributor comprising a plurality of Y-connected phase windings, a closed winding to which said Y-connectedphase winding is connected at equally spaced positions, a plurality ofcommutator segments connected to said closed winding, said segments,closed winding, and Y- connected phase windings constituting the rotorof said distributor, a second plurality of phase windings equal innumber to said Y-connected phase windings, and a plurality of brushesengaging said commutator segments at an angular spacing dependent uponthe number of said phases, said second plurality of phase windings andsaid brushes constituting the stator of said distributor.

3. A polyphase distributor system in accordance with claim 2 in whichmeans are provided for driving said Y-connected phase windings, saidclosed winding, and said commutator segments.

4. A polyphase distributor comprising a rotor consisting of a pluralityof Y-connected phase windings, a closed winding to which said phasewindings are connected at equally spaced intervals, and a plurality ofcommutator segments to which said closed winding is connected, a statorconsisting of a plurality of phase windings equal in number to saidplurality of Y-connected phase windings, and a plurality of brushesengaging the commutator segments of said rotor at an angular spacingdependent upon the number of phases of said distributor.

5. A polyphase distributor for starting a synchronous motor, saiddistributor comprising a r0- tor member consisting of a plurality ofY-connected phase windings, a closed winding to which one end of each ofsaid phase windings is connected, a plurality of commutator segmentsconnected to said closed winding, and a plurality of collector rings towhich the other ends of said phase windings are connected and adapted tobe connected to an outside power source, a stator member consisting of aplurality of brushes equal in number to said collector rings, and asecond plurality of windings having one end of each winding connected toan output circuit and their other ends connected to said brushes.

SIDNEY READ, JR.

